OTHER: Intermeshing Configuration -

• The belief that the intermeshing helicopter is a slow one has absolutely nothing to do with its configuration.
• This incorrect notion is based solely on the synchropters that Charles Kaman built.
• The first intermeshing helicopter, the Flettner Fl-282 [picture], was produced before the early Sikorsky helicopters, yet it was faster then they were.
• Wieslaw Stepniewski says "Very preliminary studies seem to indicate that placing the ABC rotors in the sychropter position should result in a somewhat aerodynamically cleaner then the coaxial ABC, and definitely a much cleaner design than the considered single-rotor types.[tip jets (Rotodyne) and vectored pusher (Piasecki)]"

• Both of the helicopter configurations being compared below have extremely rigid rotors; [ref. Sikorsky's heralded X2 and the 'slowly' developing UniCopter].
• Because of this high rotor rigidity;
• The vertical gap between the rotor disks on the Coaxial-ABC is less than that of earlier coaxials.
• The angle between the rotor masts on the Intermeshing-ABC is less than that of earlier intermeshers.

• Disk Area:
• Coaxial: The individual rotors of the Sikorsky XH-59A ABC coaxial have a radius of 18 feet. This is a disk area of 1,000 sq-ft per rotor. The upper disk is located directly above the lower disk and this results in an effective disk area of 1,000 sq-ft.
• Intermeshing: The individual rotors of the comperable intermeshing helicopter have the same radius of 18 feet. It also has a disk area of 1,000 sq-ft per rotor. The stagger between the two rotor hubs is 26% * 18 ft. = 4.7 ft. The overlap area is A = 1/2 (R² (θ - sinθ)) = 1/2 (18 * 18 (2.878 - sin(2.878))) = 1/2 (324 (2.8784 - 0.261)) = 1/2 (324 *2.617) = 424 sq-ft.. This results in an effective disk area of (1000 - 424) * 2 = 1152 sq-ft.
• Result: The disk area of the Intermesher is 15% greater than the disk area of the coaxial. Or, to put it in other words, the sq-ft. disk loading of the Intermesher is 13% less then the sq-ft. disk loading of the comperable coaxial. Of course, reduced disk loading means greater efficiency. In addition, the intermeshing rotors rotate outside forward and this means that the induced velocities are distributed more evenly across the streamtube.
• Drag:
• Both configurations have identical rotors, except that the Intermeshing rotors are13% smaller and therefore have a proportionately smaller drag.
• Plus, the location of the rotors is different. Sikorsky says that the mast that joins the two Coaxia-ABC rotorhubs contributes an additional 20% x 25% = 5% drag. The Intermeshing-ABC does not have a mast and its hubs are faired into the fuselage.

• An Intermeshing helicopter will have a 10-15% greater payload capacity than an 'identical' coaxial helicopter, at today's EW/GW ratios.
• An Intermeshing helicopter will have a 15-20% greater payload capacity than an 'identical' coaxial helicopter, at tomorrow's EW/GW ratios.
• Therefore, how can a Coaxial helicopter hope to compete head-to-head with an identical* Intermeshing helicopter?

Stepniewski-ABC comparison with Sikorsky-ABC:

• OTHER: Helicopter - Inside - Intermeshing - Pros & Cons vs. ABC Coaxial
• OTHER: Helicopter - Outside - Coaxial - Sikorsky - X2 ~ Blade Profile
• OTHER: Aerodynamic - Rotor Disk - Dual Configurations
• The Interleaving and the Side-by-side configurations will give greater payload increases than the Intermeshing configuration. However the interleaving and the side-by-side will incur the additional parasitic drag of the spars (stub wings?) and the resulting longer moment arms.

• Technical Note - Twin Rotor Hover Performance, by Franklin D. Harris ~ January 1999 Journal of the American Helicopter Society. Have on disk E: and hard copy.
• Influence of Lift Offset on Rotorcraft Performance, by Wayne Johnson ~ AHS Conference 2008. Have hard copy.

Introduction Page | SynchroLite Home Page | Electrotor Home Page | UniCopter Home Page | Nemesis Home Page | AeroVantage Home Page: